Recent increases in public concern for the environment have resulted in various government imposed environmental regulations. Among such regulations are requirements relating to the monitoring of groundwater quality. In response to these requirements, water quality analytic capabilities have been improved and water sampling equipment has been developed. Much of the previously developed sampling equipment has not been effective, however, in obtaining consistent, non-contaminated water samples that are accurately representative of the water system from which the sample is taken.
The inadequacies of the previous sampling equipment stem largely from such causes as cross-contamination between sampling sites, ineffective and inconsistent field cleaning methods, contamination due to equipment handling, and inconsistent well depth sampling. In addition to presenting sample quality problems, much of the previous equipment has been heavy and bulky and thus difficult to transport from one monitoring site to another. Finally, much of such previous equipment has proved to be complicated to operate, inordinately expensive, and impractical for sampling at remote locations where site access is severely limited.
Prior to obtaining an acceptable water sample, the well must sometimes be purged between 3 and 5 times. Depending on the size of the well and the static level of water in the well, the amount of time this purging procedure takes can be excessive. Packers have been developed which are located between the static level of the water in the well and the pump to isolate the area below the packer to reduce the amount of water which must be pumped in order to purge the well. On a high recovery well equipped with a pump and a packer, this system performs acceptably. When a pump and a packer are used in conjunction with a low recovery well, it is not possible to purge the well any quicker than the recovery rate of the well. It is not possible to form a vacuum in the volume below a packer with a standard bladder pump. Thus, in low recovery wells, the amount of time which is required to obtain an acceptable water sample is unacceptable.
In accordance with the present invention, a fluid sampling apparatus is provided for use in obtaining accurate samples of groundwater or other fluids from both high and low recovery wells. In the preferred embodiment, the pump is dedicated to a particular monitoring well or other sampling site in order to substantially avoid cross-contamination of samples from site to site and is constructed from light weight non-contaminating materials. A vented packer is provided for the fluid sample apparatus which minimizes the amount of liquid which must be purged prior to obtaining an acceptable sample. The venting of the packer enables a low recovery well to be purged at the volume rating of the pump similar to a high recovery well.
A fluid sampling pump for use in conjunction with the present invention, to which a vented packer is added to reduce the amount of liquid which must be purged prior to sampling, is disclosed in U.S. Pat. No. 4,489,779 issued Dec. 25, 1984 to Dickinson et al. and U.S. Pat. No. 4,585,060 issued Apr. 29, 1986 to Bernardin et al., the disclosures and drawings of which are hereby expressly incorporated by reference. A fluid sampling pump which has an integral packer is shown in U.S. application Ser. No. 941,693, entitled "Sampling Pump with Packer" and naming K. Lynn Niehaus as inventor. The above application is being filed concurrently herewith, the disclosure and drawings of which are hereby expressly incorporated by reference. Both applications are being assigned to the same assignee.
The preferred sampling pump is a submersible, fluid actuated pump wherein the actuating fluid is preferably a gas. A first flexible bladder member separates and isolates the interior of the pump into two chambers; a first chamber that contains the sample fluid and is in communication with both the pump inlet and outlet and a second chamber that surrounds the first chamber with the first bladder disposed therebetween. The second chamber is connected to a source of actuating gas.
A vented packer is disposed between the intake of the pump and the static level of the water in the well. The packer comprises a packer housing which has a second flexible bladder member which forms a third chamber that surrounds the packer housing. The third chamber is connected to a source of actuating gas. The conduits necessary for operating the pump below the packer pass through the packer housing and are sealed where they pass through the packer housing. The area below the packer is vented either to the area in the well casing above the static level of the water or to the atmosphere through the wellhead assembly. Prior to the pumping of groundwater, the third chamber on the packer is pressurized to expand the second bladder member. This separates the groundwater within the monitoring well into two regions, with the region below the packer being in communication with the first chamber of the pump.
The sample liquid is conveyed through the pump by alternately pressurizing and venting or relieving the pressure in the second chamber to contract and relax the first bladder member thus alternately decreasing and increasing the volume of the first chamber. Sample fluid is drawn into the first chamber from the area below the second bladder member during such increases in volume under the influence of the natural hydrostatic head of the groundwater and is discharged through the pump outlet during such decrease in volume, thereby conveying the sample fluid through the pump.
The second bladder member thus minimizes the amount of groundwater which must be purged prior to accepting a sample by isolating the intake of the first chamber of the pump from the total volume of fluid in the monitoring well or other sampling site. The venting of the area below the packer allows the pump to operate at its maximum capacity regardless of the recovery rate of the well. The components of the pump and packer are preferably composed of low cost, light weight synthetic materials that are non-corrosive and do not otherwise affect the chemical composition of the sampled fluid.
The sampling pump and packer are preferably dedicated to, and thus remain in, a particular sampling site or well without fluid pressure supplied to either the second or third chamber. The sampling site or well is substantially isolated form the above-ground surroundings by a wellhead assembly in order to reduce potential contamination during sampling. A portable controller apparatus is provided with quick-disconnect means and includes means for pressurizing the third chamber and means for alternately pressurizing and de-pressurizing the actuating fluid in the second chamber. The fluid sampling apparatus may also optionally include means for measuring the standing level of the fluid in the well.
Additional advantages and features of the present invention will become apparent from the following description and the appended claims taken in conjunction with the accompanying drawings.